Kimi Raikkonen set the fastest time in both of Friday's practice sessions for Sunday's Chinese Grand Prix.
The Ferrari driver clocked a time of one minute, 36.607 seconds to edge out Fernando Alonso, with Ferrari's Felipe Massa third and Lewis Hamilton fourth.
Alonso's McLaren team-mate Hamilton could clinch the drivers' title in Shanghai this weekend.
Hamilton has a 12-point lead over Alonso after being cleared of alleged erratic driving in Japan.
After pipping Alonso in the morning practice session, Raikkonen left it until the very end of the afternoon run to again overcome the Spaniard by the narrowest of margins.
Raikkonen dropped to fifth before pulling out an impressive final burst, with barely two minutes remaining.
606: DEBATE
Massa went off the track during both sessions.
Hamilton also skirted on to the gravel at turn two after the rear of his car briefly snapped out of control but the Briton managed to continue.
There is another free practice session on Saturday morning before qualifying on the 3.4-mile Shanghai International circuit.
"It was a good day, even if Friday results have to be considered for what they are," said Raikkonen.
"I'm expecting a close fight tomorrow."
Alonso, meanwhile, insists he has not lost all hope of retaining the title despite Hamilton being within touching distance of securing it in his debut season.
"I will not give up," said Alonso.
"I'm more relaxed than normal. It's not up to me anymore. I need a combination of results to help me."
Chinese Grand Prix Friday first practice times:
1. Kimi Raikkonen (Fin) Ferrari 1:37.024
2. Fernando Alonso (Spa) McLaren-Mercedes 1:37.108
3. Felipe Massa (Brz) Ferrari 1:37.128
4. Lewis Hamilton (GB) McLaren-Mercedes 1:37.210
5. Nico Rosberg (Ger) Williams-Toyota 1:37.707
6. Robert Kubica (Pol) BMW Sauber 1:38.055
7. Jarno Trulli (Ita) Toyota 1:38.208
8. Giancarlo Fisichella (Ita) Renault 1:38.217
9. Kazuki Nakajima (Jpn) Williams-Toyota 1:38.270
10. Nick Heidfeld (Ger) BMW Sauber 1:38.445
11. Heikki Kovalainen (Fin) Renault 1:38.551
12. Ralf Schumacher (Ger) Toyota 1:38.661
13. David Coulthard (GB) RedBull-Renault 1:38.700
14. Jenson Button (GB) Honda 1:38.942
15. Rubens Barrichello (Brz) Honda 1:38.945
16. Takuma Sato (Jpn) Super Aguri-Honda 1:39.238
17. Vitantonio Liuzzi (Ita) Toro Rosso-Ferrari 1:39.497
18. Mark Webber (Aus) RedBull-Renault 1:39.535
19. Anthony Davidson (GB) Super Aguri-Honda 1:39.539
20. Sebastian Vettel (Ger) Toro Rosso-Ferrari 1:39.898
21. Sakon Yamamoto (Jpn) Spyker-Ferrari 1:40.126
22. Adrian Sutil (Ger) Spyker-Ferrari 1:40.149
Chinese Grand Prix Friday second practice times:
1. Kimi Raikkonen (Fin) Ferrari 1:36.607
2. Fernando Alonso (Spa) McLaren-Mercedes 1:36.613
3. Felipe Massa (Brz) Ferrari 1:36.630
4. Lewis Hamilton (GB) McLaren-Mercedes 1:36.876
5. Jarno Trulli (Ita) Toyota 1:37.151
6. Mark Webber (Aus) RedBull-Renault 1:37.450
7. Ralf Schumacher (Ger) Toyota 1:37.524
8. David Coulthard (GB) RedBull-Renault 1:37.617
9. Nico Rosberg (Ger) Williams-Toyota 1:37.646
10. Giancarlo Fisichella (Ita) Renault 1:37.970
11. Heikki Kovalainen (Fin) Renault 1:38.062
12. Jenson Button (GB) Honda 1:38.205
13. Rubens Barrichello (Brz) Honda 1:38.304
14. Robert Kubica (Pol) BMW Sauber 1:38.379
15. Nick Heidfeld (Ger) BMW Sauber 1:38.388
16. Alexander Wurz (Aut) Williams-Toyota 1:38.531
17. Anthony Davidson (GB) Super Aguri-Honda 1:38.975
18. Vitantonio Liuzzi (Ita) Toro Rosso 1:39.065
19. Adrian Sutil (Ger) Spyker 1:39.224
20. Takuma Sato (Jpn) Super Aguri-Honda 1:39.360
21. Sebastian Vettel (Ger) Toro Rosso 1:39.404
22. Sakon Yamamoto (Jpn) Spyker 1:40.051
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